Method of recording fingerprints of human body



United States Patent 3,492,140 METHOD OF RECORDING FINGERPRINTS OF HUMAN BODY Satoru Honjo, Odawara-shi, and Takeo Tsuyuki,

Ashigarakami-gun, Kanagawa-ken, Japan, assignors to Fuji Shashin Film Kabushiki Kaisha, Ashigarakami-gun, Kanagawa-ken, Japan No Drawing. Continuation-impart of application Ser. No. 350,556, Mar. 9, 1964. This application Nov. 24, 1967, Ser. No. 685,332

Int. Cl. B41m 3/00 US. Cl. 117-.5 3 Claims ABSTRACT OF THE DISCLOSURE A method of recording fingerprints of the human body which comprises uniformly charging electrostatically an insulating coating provided on a conductive backing, placing a hand or palm to be recorded in contact with said charged surface, whereby those areas where the human skin contacted lose their charge, and then applying an electroscopic material on that surface, characterized in that said insulating coating composition comprises 100 parts by weight of film forming resinous material and to 50 parts by weight of finely divided colloidal silica.

This application is a continuation-in-part of application Ser. No. 350,556, filed Mar. 9, 1964, now abandoned.

This invention relates to method of recording fingerprints of human body.

Visible recording can be made on an electrically in sulating coating provided on a backing, the conductivity ofwhich is higher than that of the coating, in two ways. First, an electrically conductive material such as a metal type material is brought into contact with the coating that has been previously charged uniformly. The electrostatic charge on the contacted area is instantaneously discharged through the said conductive material, thus forming an electrostatic latent image (imagewise discharge method).

The other process is reversal one to the first, that is; an electrically conductive material, which is connected to a positive or negative electrode of a DC. high voltage source, is brought into close-contact with the said insulating coating, then the contacted area is selectively charged (imagewise charging method).

An electrostatic image thus formed can be converted to a visible image by an ordinary development Well known in the field of electrophotography.

Such recording processes are useful in high-speed printing or recording connected with electronic computers or business machines. As a unique application of the imagewise discharge method described above, electrostatic fingerprint recording can be accomplished utilizing human body as the discharging medium.

In the past, coatings comprising only insulating filmforming materials, have been utilized for these purposes, which have been found unsatisfactory for com mercial use, because they were liable to stick together and blocking came about during storage, especially in warm atmosphere, and they could not be inscribable with ordinary writing means. Moreover when they were utilized in fingerprint recording, they could not give stable and clear reproduction of fingerprints impressed thereon.

It is a principal object of this invention to provide a new and improved material for electrostatic recording and especially for electrostatic fingerprint recording. The coating has good aging properties and is resistant to heat and moisture that would normally be encountered during storage, and it has a mat surface inscribable with ordinary writing instruments. Another remarkable feature of the present invention is that the quality of reproduced image obtained by the imagewise discharge method, and especially by fingerprint impression, upon the coating prepared according to the present invention is far better than those obtained on the prior coatings.

The present invention utilizes a new coating composition comprising electrically insulating film-forming materials and fine particles of colloidal silica (S 0 homogeneously dispersed in the said film-forming materials, such a coating composition can be prepared by mixing SiO fine particles and insulating binding material dissolved in suitable solvents, utilizing mixing apparatus such as ball mill or those well-known in the art.

'Particle size of Si0 used affects the electrical property and surface structure of the resulting coating, the best result is obtained with those of extremely fine particle size, known as colloidal silica.

Almost all of insulating film-forming materials are available, for example, polyvinyl chloride, polyvinylidene chloride, polyvinylchloride/vinylidene chloride, polyvinyl chloride/ acetate, polyvinyl acetate, poly(styrene/butadiene), polyalkylacrylates, polyalkylmethacrylates, poly(vinylacetate/alkylacrylates), cellulose acetate, cellulose acetobutyrate, linear polyester resins, unsaturated polyesters, alkyd resins and other heat-setting polyesters, silicone resins, modified alkyd resins, modified silicone resins, phenolformaldehyde resins, xyleneformaldehyde resins, and the mixtures of these; pasticizers may be added, if necessary.

Content of colloidal silica (SiO in the recording layer affects the insulating and other properties; excessive amount makes the layer fragile and the rate of charge leakage very rapid; too small amount fails to improve the recording property and to provide a mat surface. SiO; powders from 10 parts to 50 parts per parts of film-forming material give, in general, satisfactory results.

Photoconductive materials such as ZnO or organic photoconductors may be added in minor quantity, the layer thus composed may be discharged under strong illumination of light, when one needs to erase a charge pattern once formed.

Base sheets must have higher electrical conductivity than that of the coating layer thereon; metal sheets, metal foil laminated materials or insulating materials bearing conductive surface layer and ordinary paper are available. When the base sheet is paper, pretreatment with a noninsulating film-forming material may be applied for the purpose of inhibition of the penetration of the coating solution into the porous structure of the paper. The impregnation of the insulating material into the base sheet, without applying the pretreatment, results in an extreme deterioration of the recording characteristics of the material, probably because of the decrease of the electrostatic capacity of the recording layer, which leads to the decrease of the of electrostatic charge density on the surface. Following low-resistance film-forming materials are available. Polyvinyl alcohol, maleic anhydride or maleic acid copolymers with vinylalkylethers, with vinyl acetate, with styrene, polyvinyl pyrolidone, poly(vinyl pyrolidone/ vinyl acetate), polyacrylic acid, polymethacrylic acid, carboxymethyl cellulose, Na alginate, etc. Addition of hygroscopic inorganic salt or plasticizers such as glycerin, glycol, may be recommended under low relative humidity conditions.

Imagewise charging can be accomplished by bringing characters or figures made of conductive material, which is connected to a high voltage D.C. electrode, in close contact with a recording layer. The voltage required to obtain clear and distinct images varies with the property of the layer, but, in general, several hundreds to one thousand volts is necessary.

In imagewise discharge method, the previous uniform charging of the layer can be carried out by subjecting the layer to a corona discharge. On the uniformly charged layer are pressed fingers or hand.

The developing method of the latent image is common in these two methods, but in ordinary applications, such developments are used that electroscopic colored toner particles adhere to the charged region in the former method, and to the discharged region in the latter. Therefore, in the imagewise charging method, the signs of charge should be different between the toner particles and the image area. On the other hand, in the case of imagewise discharging method, the remaining charge on the layer and the toner particles used should be equal. Liquid, cascade, magnetic blush, or powder cloud developments may be used.

It is very difiicult, at present, to interpret theoretically the favorable effect of SiO addition of other powderformed materials such Ti talc, ZnO, BaTi0 BaSO or clay could not improve the recording properties at all, or so remarkably as fine particles of SiO The remarkable increase of image density obtained by imagewise discharge method suggests the increase of surface charge density. The minute coarseness of the surface might be favorable for rapid discharge when the surface is touched with a conductive material.

Anyhow, SiO -containing insulating layers give images of excellent quality, with high image density and low background fog density by both methods of recording. Such favorable behavior is not affected by high relative humidity of the environment.

EXAMPLE I Parts by wt. Polyvinyl chloride/ acetate (mol ratio 70:30) degree of polymerization 300 100 Colloidal silica (Trade name Aerosol produced by Degussa 00., West Germany) 20 Trichloroethylene 100 Toluene 50 Xerox type toner 10 Reduced iron powders, (particle size l50 200 t) 1000 The comparison of these two sheet was as follows:

Initial surface potential Half time (volt) for voltage Image quality PVC/Ac-SiO 250 About 4 min Good, low back ground density. PVC/Ac 390 About 30 min Fair, high back ground density.

The table shows that a high initial voltage or slow leakage does not necessarily guarantee a good image quality in the present process.

EXAMPLE II Silicone resin varnish (Trade name, Shin-etsu Silicon KR-25'4, nonvolatile 30%, produced by Shin-etsu Chemical Ind., Japan) 150 Colloidal silica (aerosil) l5 Toluene 150 Initial surface potential Halftime (volt) for voltage Image quality KR-254-Si0z... 185 About 6 min Excellent, high image density, very low background density. KR-254 350 About 15 min-.. Fair-poor, low image density, high background density.

EXAMPLE III Silicone resin varnish (non-volatile 70%) Trade name Shin-etsu Silicon KR-Zll 100 Polyvinyl acetate/butyl acrylate (mol ratio, :20) 30 Colloidal silica (Aerosol) 25 Ethyl acetate 40 Toluene A homogeneous mixture of the above composition was applied on a paper base as described in Example II. The coating layer absent of SiO was strongly tacky and abandoned.

The layer showed 400 volts of initial surface potential, and about 10 min. of half time, and when subjected to imagewise charging and discharging processes, images of excellent quality were obtained. The surface of the coating was slightly rough and inscribable with pencil or other ordinary writing means.

EXAMPLE IV The two sheets described in Examples I and II gave 6 clear and distinct images by image-wise charging process.

EXAMPLE V Polyvinyl acetate/butyl acrylate was replaced with the same amount of polyvinyl acetate.

EXAMPLE VI Polyvinyl(acetate/butyl acrylate) was replaced with 60 parts of styrenated alkyd resin varnish (trade name Styresol 4250 produced by Japan Reichhold Chemicals Co., non-volatile 50%.)

EXAMPLE VII The coating composition of Example VI was applied onto an aluminium-laminated paper base.

What we claim is:

1. A method of recording fingerprints of human body comprising uniformly charging electrostatically an insulating coating provided on a conductive backing, placing a hand or palm to be recorded in contact with said charged surface, whereby those areas where the human skin contacted lose their charge, and then applying an electroscopic material on that surface, which is characterized by that said insulating coating composition comprising 100 parts by weight of film forming resinous material and 10 to 50 parts by weight of finely divided colloidal 10 silica.

2. A method as claimed in claim 1 wherein said conductive backing is a paper.

has a surface layer consisting of a lower electrical resistance.

References Cited UNITED STATES PATENTS 3,408,217 10/1968 Obuchi 1l70.5

FOREIGN PATENTS 290,926 8/ 1961 Japan.

MURRAY KATZ, Primary Examiner US. Cl. X.R.

3. A method as claimed in claim 2 wherein said paper 15 117- 17.5, 155; 118-315; 346-1, 74, 135 

